1. Field of the Invention
The present invention relates to a control device for controlling the amount of charging or discharging of a battery installed in a hybrid vehicle in order to protect the battery.
2. Description of the Related Art
A hybrid vehicle, which comprises not only an engine but also an electric motor as the drive source, has been known in the art. Such hybrid vehicles are classified into two types: series hybrid vehicles and parallel hybrid vehicles. A series hybrid vehicle is a vehicle in which a motor is operated using the electrical power output of a generator which is driven by an engine, and the motor drives the wheels of the vehicle.
Accordingly, the engine and the wheels are not mechanically connected to each other; therefore, the engine can be continuously operated at a predetermined revolution rate at which high fuel efficiency and low emissions can be achieved.
In contrast, in the case of a parallel hybrid vehicle, driving operation by the drive shaft of an engine is assisted by a motor connected to the engine. The motor is also used as a generator, and the generated electrical energy is not only stored in a battery device but is also used for electrical equipment installed in the vehicle.
Accordingly, the load applied to the engine is reduced; therefore, as in the case of a series hybrid vehicle, better fuel efficiency and lower emissions can be achieved when compared with a conventional vehicle having only an engine.
As examples of the aforementioned parallel hybrid vehicles, a hybrid vehicle has been known in which a motor is directly connected to the output shaft of an engine so that the motor assists the output power of the engine, and the motor functions as a generator during deceleration, the output of the generator being stored in a battery or the like, and another hybrid vehicle has also been known in which one of an engine and a motor outputs driving power or both an engine and a motor output driving power, and a generator is provided separately.
In such hybrid vehicles, for example, the power of the engine is assisted using the electric motor during acceleration, whereas during deceleration, the battery or the like is charged using a deceleration regenerative operation. According to various control operations including the above, the electrical energy of the battery (hereinafter referred to as state of charge) is maintained while also satisfying the driver""s demands.
When electrical power required by electrical equipment installed in a hybrid vehicle exceeds electrical power generated by the motor, the battery used in the hybrid vehicle supplies electrical power to the electrical equipment to make up for the shortfall. Accordingly, when the engine is in an idling mode, the electrical power consumed by the electrical equipment tends to exceed electrical power generated by the motor; as a result, a problem is encountered in that the battery tends to be in an over-discharged state. When the battery of the hybrid vehicle is in an over-discharged state, the vehicle must be driven solely by the engine; as a result, a problem is experienced in that fuel efficiency is degraded, or drive power is decreased. Furthermore, because hybrid vehicles may be used year-round, and also because hybrid vehicles may be used in cold areas, the vehicles may be subjected to a wide range of temperature variation, and in general, the output voltage of a battery tends to fall at low temperature, another problem is encountered in that the battery deteriorates and the operational life thereof may be shortened if the battery is continuously used in a manner as it would be at under normal temperatures.
In consideration of the above circumstances, an object of the present invention is to provide a control device for a hybrid vehicle, which measures the degree of over-discharge of a battery depending on the temperature of the battery, and which controls the amount of charge/discharge in accordance with the measured degree of over-discharge so as to protect the battery.
In order to solve the above problems and to achieve the above object, the present invention provides a control device for a hybrid vehicle which comprises an engine outputting driving power therefor, a motor connected to the engine and outputting auxiliary driving power for assisting the output of the engine, a battery supplying electrical power to the motor as well as storing electrical energy generated by the operation of the motor as a generator, and electrical loads being supplied energy generated from the motor and electrical energy from the battery, the control device comprising: a battery protection section for increasing the revolution rate of the engine or for stopping electrical supply to the electrical loads when it is determined that the battery is in an over-discharged state; a state of charge measuring section for measuring the state of charge of the battery; and a temperature measuring section for measuring the temperature of the battery, wherein the battery protection section increases the revolution rate of the engine in an idling mode when the state of charge of the battery is equal to or less than a first predetermined value which is determined depending on the temperature of the battery measured by the temperature measuring section, and the battery protection section stops supplying electrical power to the electrical loads when the state of charge of the battery is equal to or less than a second predetermined value which is determined depending on the temperature of the battery measured by the temperature measuring section.
According to the above control device of the present invention, because a module included in the battery is provided with a temperature sensor, and a threshold for determining whether the battery is in an over-discharged state is changed depending on the temperature of the battery measured by the battery sensor so that it is determined that the battery is in an over-discharged state at an earlier stage when the temperature of the battery is relatively low than when the temperature is moderate, an effect is obtained that a decrease in battery voltage when the battery is in an over-discharged state, which tends to occur under low temperature conditions, can be preferably prevented beforehand, and consequently, deterioration of the battery is delayed.
In the above control device of the present invention, supplying electrical power to the electrical loads may be stopped by disconnecting electrical connection to a converter which is provided in an electrical power supply path connecting the battery with the electrical loads.
Accordingly, because the electrical connection to the converter is disconnected when supplying electrical power to the electrical loads should be stopped, an effect is obtained that the electrical power supply can be simply stopped.
In the above control device of the present invention, the hybrid vehicle may further comprise a sub-battery for supplying electrical power to the electrical loads, and the converter may be provided in an electrical power supply path connecting the battery with the sub-battery.
Accordingly, an effect is obtained that the electrical power supply to the electrical loads can be continued even when the electrical connection to the converter is disconnected.
In the above control device of the present invention, the second predetermined value may be set to be smaller than the first predetermined value.
Accordingly, because the second predetermined value as the threshold for the state of charge is set to be smaller than the first predetermined value, an effect is obtained that the battery can be stepwise prevented from being in an over-discharged state as the state of charge decreases.
The present invention provides another control device for a hybrid vehicle which comprises an engine outputting driving power for the vehicle, a motor connected to the engine and outputting auxiliary driving power for assisting the output of the engine, a battery supplying electrical power to the motor as well as storing electrical energy generated by the operation of the motor as a generator, electrical loads being supplied energy generated from the motor and electrical energy from the battery, and a converter provided in an electrical power supply path connecting the battery with the electrical loads, the control device comprising: an engine stop section for stopping or starting the engine automatically depending on a predetermined operation state; and a battery protection section for stopping electrical power supply to the electrical loads when the engine is in an idling mode and when it is determined that the battery is in an over-discharged state, and for disconnecting electrical connection to the converter provided in the electrical power supply path connecting the battery with the electrical loads when the engine is in an automatically stopped state and when the state of charge of the battery is equal to or less than a first predetermined value.
According to the above control device of the present invention, because the electrical power supply to the electrical loads is stopped when the engine is in an idling mode and when it is determined that the battery is in an over-discharged state, the entire generated power can be used for charging. In addition, because the electrical connection to the converter provided in the electrical power supply path connecting the battery with the electrical loads is disconnected when the engine is in an automatically stopped state and when the state of charge of the battery is equal to or less than the first predetermined value, an effect is obtained that further discharge from the battery can be prevented.
In the above control device of the present invention, the vehicle may further comprise a contactor for connecting or disconnecting electrical power supply from the battery to the motor, and the battery protection section may disconnect the contactor when the engine is in an automatically stopped state and when the state of charge of the battery is equal to or less than a second predetermined value.
Accordingly, because the contactor is disconnected when the engine is in an automatically stopped state and when the state of charge of the battery is equal to or less than the second predetermined value, an effect is obtained that discharge from the battery can be completely stopped.
In the above control device of the present invention, the second predetermined value may be the lowest state of charge with which restarting of the engine is possible.
Accordingly, because the second predetermined value is set to be the lowest state of charge with which restarting of the engine is possible, an effect is obtained that the engine can be reliably restarted when the conditions for restarting of the engine are satisfied.
In the above control device of the present invention, the second predetermined value may be set to be smaller than the first predetermined value.
Accordingly, because the second predetermined value as the threshold for the state of charge is set to be smaller than the first predetermined value, an effect is obtained that the battery can be stepwise prevented from being in an over-discharged state as the state of charge decreases.